Method for a mobile to register with one or more cell sites and method for paging the mobile

ABSTRACT

A wireless communication system includes switching infrastructure (150) and at least one location area (&#34;LA&#34;) having a multiplicity of cells (the &#34;multiple-cell LA&#34;) (103). When a mobile (100) enters a cell belonging to the multiple-cell LA, the mobile is arranged with a cell-registration feature that enables it to register with the serving cell site, thus forming a registration with the cell site. When the mobile enters a further cell belonging to the multiple-cell LA, the mobile registers with the corresponding further cell site, thus forming a registration with the further cell site. When the switching infrastructure receives a call attempt towards the mobile, the switching infrastructure pages the mobile in only those cells in which a cell registration exists for the mobile.

REFERENCE TO PRIOR PROVISIONAL APPLICATION

The applicant hereby claims the priority benefit of prior provisionalapplication serial number 60/001,685, filed Jul. 31, 1995, by ArielPashtan and Israel A. Cimet, the same inventors as in the presentapplication, and which prior provisional application is herebyincorporated by reference verbatim, with the same effect as though theprior provisional application were fully and completely set forthherein.

FIELD OF THE INVENTION

This application relates to wireless communication systems including,but not limited to, a method for a mobile to register with one or morecell sites and a method for paging the mobile.

BACKGROUND OF THE INVENTION

It is known that modern wireless communication systems, such as digitalcellular systems, including Global System for Mobile Communication(hereinafter "GSM"), utilize mobility management and call processingprocedures.

It is also known that radio frequencies are a scarce resource for radiocommunication, and new methods to improve the efficiency of its use areconstantly sought. A typical wireless system keeps track of the locationof a mobile by creating different geographical areas called "locationareas". The term "location area" is hereinafter alternately referred toas "LA." A mobile that moves between two location areas sends a messagecalled a "location update" to inform the system of its new location.

When a mobile enters a new location area, it performs a location updateprocedure, that is, it informs the wireless communication system'sswitching infrastructure of its new LA. This procedure is referred to asa SWITCH LOCATION UPDATE (hereinafter "SLU").

A typical location area will consist of one or more cells, each cellcomprising the coverage area of its corresponding serving cell site.Using existing technology, when a mobile is paged, all cells in thecurrent LA are paged, even though the mobile is just in one cell, thusresulting in significant RF bandwidth being wasted. Decreasing the LAgeographical sizes will not improve the problem, since now the mobilehas to register more often thus incurring both an RF utilizationincrease as well as an additional overhead on the signaling required inthe infrastructure.

As a result, there is a need for a new location update procedure formobiles in wireless communication systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a wireless communication system that isuseful for demonstrating a method for a mobile to register with one ormore cell sites and a method for paging the mobile, in accordance withthe present invention. As shown, the wireless communication systemincludes switching infrastructure 150, a mobile 100, and at least one LA103 having a multiplicity of cells (the "multiple-cell LA"). Asexplained below, the mobile includes a cell-registration feature thatenables it to register with one or more cell sites of the multiple-cellLA.

FIG. 2 is a block diagram of a typical cell 1 of the wirelesscommunication system, the cell including a serving cell site 11.

FIG. 3 is a flow diagram used by a mobile to register with one or morecell sites.

FIG. 4 is a flow diagram used by a cell site to register the mobile.

FIG. 5 is a flow diagram used by the switching infrastructure to controlthe cell-registration feature in the mobile.

FIG. 6 is a flow diagram used by the switching infrastructure to pagethe mobile.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Briefly, the present invention generally is directed to a wirelesscommunication system that includes switching infrastructure, at leastone mobile, and at least one location area having a multiplicity ofcells, hereinafter referred to as the "multiple-cell LA." In particular,the present invention is directed to a method for the mobile to registerwith one or more cells as it travels through the multiple-cell LA. Theinvention further includes a method for the switching infrastructure ofthe wireless communication system to page the mobile within themultiple-cell LA.

In one aspect of the invention, when the mobile enters a cell belongingto the multiple-cell LA, the mobile is arranged with a cell-registrationfeature that enables it to register with the serving cell site, thusforming a mobile registration with the cell site. When the mobile entersa further cell belonging to the multiple-cell LA, the mobile registerswith the corresponding further cell site, thus forming a mobileregistration with the corresponding further cell site. Moreover, whenthe switching infrastructure receives a call attempt towards the mobile,the switching infrastructure pages the mobile in only those cells inwhich a registration exists for the mobile.

In a further aspect of the invention, when the mobile has remainedwithin the cell for a first time period, it re-registers with theserving cell site, thus re-forming a mobile registration with the cellsite. Likewise, each cell site in which a registration exists for themobile discards the mobile registration after a second time period. Inone embodiment, the first time period and the second time period areeach based on the average time the mobile requires to traverse a typicalcell, with the two time periods being approximately equal.

In a still further aspect of the invention, the mobile contains a listof recently-visited cells. Upon entering a cell, when the mobiledetermines that the cell is NOT on the list of recently-visited cells,it registers with the serving cell site and adds the cell to the list ofrecently-visited cells. Conversely, when the mobile determines that thecell IS on the list of recently-visited cells, it does NOT register withthe serving cell site, and does NOT add the cell to the list ofrecently-visited cells.

In another aspect of the invention, the mobile includes a call activitythat varies with time, and the mobile's cell-registration feature may beselectively enabled by the switching infrastructure based on the callactivity for the mobile. When the call activity for the mobile exceeds afirst threshold, the switching infrastructure enables thecell-registration feature in the mobile. Conversely, when the callactivity for the mobile is less than a second threshold, the switchinginfrastructure disables the cell-registration feature in the mobile.

In still another aspect of the invention, when the switchinginfrastructure receives a call attempt towards the mobile and thecell-registration feature is enabled for the mobile, the switchinginfrastructure pages the mobile in only those cells in which aregistration exists for the mobile; otherwise, when thecell-registration feature is not enabled for the mobile, the switchinginfrastructure pages the mobile in the multiplicity of cells.

Referring now to FIG. 1, there is shown a wireless communication systemincluding switching infrastructure 150 and including one or morelocation areas 101, 103, 105, with each location area being designated"LA." The LA's 101, 103 and 105 are alternately designated as LA1, LA2,and LA3, respectively. As shown, the wireless communication systemincludes at least one LA, namely LA2, that includes a multiplicity ofcell sites (the "multiple-cell LA"). Also shown is a typical mobile 100that, as explained below, is arranged with a cell-registration featurethat enables it to register with one or more cell sites. Further, themobile includes a call activity that varies with time. As shown, themultiple-cell LA 103 includes 9 cells respectively designated 1-9.Further, each cell 1-9 includes a corresponding serving cell site, asdiscussed with FIG. 2 below.

As shown, the switching infrastructure 150 is linked to the LA1, LA2,and LA3 respectively by links 151, 153 and 155. Although the wirelesscommunication system is depicted in FIG. 1 as containing three LA's 101,103 and 105, the invention is equally applicable to wirelesscommunication systems having any number of LA's, provided that at leastone LA includes a multiplicity of cells.

In a first embodiment, the wireless communication system of FIG. 1 is aGSM system.

In a second embodiment, the wireless communication system of FIG. 1 isan Integrated Dispatch Enhanced Network ("iDEN") system.

In a third embodiment, the wireless communication system of FIG. 1 is aUnited States Digital Cellular ("USDC") system.

Moreover, in still other embodiments, the present invention may beapplied to any wireless communication system that includes at least onemultiple-cell location area.

Referring now to FIG. 2, there is shown a block diagram of a typicalcell 1 of the wireless communication system, the cell including itscorresponding serving cell site 11. In this view, the mobile 100 isdepicted as being located within cell 1. As shown, the cell site 11 iscoupled to the switching infrastructure 150 by means of the link 153.Also as shown, the mobile 100 contains a list 201 of recently-visitedcells.

Returning momentarily to FIG. 1, suppose the mobile 100 travels from LA1to LA2 to LA3 and, while in LA2, further suppose the mobileconsecutively travels through multiple cells. In accordance with thepresent invention, the mobile is arranged with a cell-registrationfeature that enables it to register with each cell site in its path asit travels through LA2.

Referring now to FIG. 3, there is shown a flow diagram used by themobile to register with one or more cell sites in its journey throughLA2.

The process begins at step 301. In step 305, after leaving the (old)LA1, the mobile enters a cell in the (new) LA2. This step 305 isequivalent to the mobile entering a cell belonging to the multiple-cellLA2. In step 307, the mobile performs a SLU; that is, the mobileregisters in the new LA2 with the switching infrastructure 150.

In step 309, the mobile determines when the cell is on the list ofrecently-visited cells. If the determination to this step 309 isnegative, the mobile proceeds to step 311; otherwise, if thedetermination to this step 309 is positive, the mobile proceeds to step315.

When the mobile determines in step 309 that the cell site is NOT on thelist of recently-visited cell sites, the process goes to step 311, wherethe mobile registers with the corresponding cell site, thus forming aregistration for the mobile with the corresponding cell site. In step313, the mobile adds the cell site to the list of recently-visited cellsites. The process then goes to step 315.

As mentioned above, when the mobile determines in step 309 that the cellIS on the list of recently-visited cells, the process OMITS (that is,does NOT perform) step 311 (registering with cell site) and step 313(adding the cell to list), and goes DIRECTLY to step 315.

In step 315, the process determines when the mobile has remained withinthe cell for a first time period. When the mobile determines that it hasremained within the cell for the first time period, the determinationfrom step 315 will be positive, and the process returns to step 311,where it re-registers with the corresponding cell site, thus re-forminga registration for the mobile with the corresponding cell site.Otherwise, the process proceeds to step 317.

In step 317, the process determines when the mobile has entered afurther cell belonging to the same LA, that is, the multiple-cell LA2.

When the determination from step 317 is positive (that is, the mobilehas entered a further cell in the same LA), the process returns to step309. In step 309, assuming the further cell is NOT on the list ofrecently-visited cells, then the determination from step 309 will benegative, and the process will proceed to step 311, where the mobileregisters with the corresponding further cell site, thus forming aregistration for the mobile with the corresponding further cell site.

Ultimately, when the mobile does NOT remain in the cell for a first timeperiod AND when the mobile does NOT enter a further cell in the same LA,then the determination of steps 315 and 317 respectively will BOTH benegative, and the mobile will leave the LA, step 319. The process willthen end, step 321.

Referring now to FIG. 4, there is shown a flow diagram used by each cellsite in the multiple-cell LA2 to register the mobile.

The process starts, step 401. In step 403, when the mobile registerswith the cell site, the cell site records the registration for themobile, that is, the mobile's identification, or "ID".

In step 407, the cell site discards the registration after a second timeperiod elapses. Thus, each cell site in which a registration exists fora given mobile will discard the registration, that is, the mobile's ID,after the expiration of the second time period. The process then ends,step 409.

The first time period and the second time period are both operatordefined. In one embodiment, the first time period is based on theaverage time the mobile requires to traverse a typical cell; as well,the second time period is based on the average time the mobile requiresto traverse a typical cell. Also, typically the first time period isless than the second time period.

The cell-registration feature thus allows the mobile 100 to form aregistration with each cell that it visits as it travels through themultiplicity of cells comprising LA2. Further, in accordance with thepresent invention, the mobile's cell-registration feature may beselectively enabled by the switching infrastructure 150 based on thecall activity of the mobile, wherein the call activity of the mobilevaries with time. It will be appreciated that the call activitycorresponds to the rate of mobile-terminated call attempts.

Referring now to FIG. 5, there is shown a flow diagram used by theswitching infrastructure 150 to control the cell-registration feature inthe mobile based on the call activity of the mobile.

The process starts, step 501.

In step 503, the process determines the call activity for the mobile.

In step 515, the process determines when the call activity for themobile exceeds a first threshold. It will be appreciated that the firstthreshold corresponds to a relatively high rate of attempts to terminatecalls in the mobile 100.

When the process determines that the call activity for the mobileexceeds the first threshold, then the process goes to step 517, where itenables the cell-registration feature in the mobile. The process thengoes to step 525.

In step 525, the process determines when the call activity for themobile is less than a second threshold. It will be appreciated that thesecond threshold corresponds to a relatively low rate of attempts toterminate calls in the mobile 100.

When the process determines that the call activity for the mobile isless than the second threshold, then the process goes to step 527, whereit disables the cell-registration feature in the mobile.

The process then ends, step 531.

The first (high) threshold and the second (low) threshold are bothoperator defined. In one embodiment, the first threshold is greater thanthe second threshold. In an alternate embodiment, the first threshold isapproximately equal to the second threshold.

Referring again to step 515, it will be appreciated that substantiallyequivalent results would be achieved if step 515 determined when thecall activity for the mobile exceeds OR EQUALS the first threshold.

Also, referring again to step 525, it will be appreciated thatsubstantially equivalent results would be achieved if step 525determined when the call activity for the mobile is less than OR EQUALSthe second threshold.

By controlling the cell-registration feature in the mobile based on themobile's call activity, the operation of the mobile cell-registrationfeature is advantageously improved by minimizing the radio frequency("RF") overhead required to register the mobile with the cell site. As aresult, only mobiles having a relatively high rate of attemptedmobile-terminated calls and corresponding high rate of wirelesscommunication system paging will incur a cell registration RF overhead.

Referring now to FIG. 6, there is shown a flow diagram used by theswitching infrastructure 150 to page the mobile 100 as it travels in themultiple-cell LA2. It will be recalled (with momentary reference to thediscussion of FIGS. 3-4 above) that the mobile 100 includes acell-registration feature that allows the mobile to form a registrationwith each cell that it visits as it travels through LA2. It will also berecalled (with momentary reference to the discussion of FIG. 5 above)that the cell-registration feature of the mobile may be selectivelyenabled by the switching infrastructure 150.

The process starts, step 601.

Upon receiving a call attempt towards the mobile by the switchinginfrastructure, step 603, the process goes to step 605. In step 605, theswitching infrastructure determines when the cell-registration featureis enabled for the mobile.

When step 605 determines that the cell-registration feature IS enabledfor the mobile, the process goes to step 617. In step 617, the switchinginfrastructure pages the mobile in ONLY those cells in which aregistration exists for the mobile. The process then ends, step 650.

Conversely, when step 605 determines that the cell-registration featureis NOT enabled for the mobile, the process goes to step 672. In step627, the switching infrastructure pages the mobile in ALL cellsthroughout LA2, that is, in the multiplicity of cells comprising LA2.The process then ends, step 650.

In practice, the cell-registration process can be viewed in terms of themobile 100 performing a new CELL LOCATION UPDATE ("CLU") procedure byregistering in the visited cells of its current location area.Thereafter, when paged in the location area, only the visited cells willbe paged.

Again, with reference to FIG. 1, suppose the mobile enters LA2 in cell1, and sequentially traverses cell 2 and cell 3 in its path across LA2.A mobile performs a CLU in each of the traversed cells 1, 2 and 3. If acall attempt is made towards the mobile while the mobile is in cell 3,the only cells that will be paged are cell 1, cell 2, and cell 3.

Further, the CLU procedure can be performed by the mobile whenever it isturned on, or it moves into a new cell and starts listening to the newserving cell site. This new procedure requires a CLU message to be sentby the mobile to the serving cell site. In a typical wirelesscommunication system, this message could be sent on a random accesschannel or on a dedicated signaling channel. The CLU message would beprocessed at the cell site, and an acknowledgment would be sent back tothe mobile. Therefore, a typical mobile would require 2-4 messages toperform a cell-registration. As mentioned above in the discussion ofstep 315, the mobile will send a periodic cell-registration message ifthe mobile remains in the same cell for a period of time defined as CLUPERIOD ("CLUP"). Moreover, the mobile still performs the SLU when itmoves to a different LA.

The corresponding cell-registration CLU algorithm for the mobile is:

IF the mobile has just camped on a new cell

THEN send a CLU message to the corresponding new cell site

ELSEIF CLUP has elapsed

THEN send a CLU message to the current camped-on cell site

ELSEIF the mobile was switched on

THEN send a CLU message to the current camped-on cell site

Unlike the SLU, the CLU is registered only with the serving cell site.The CLU message contains the mobile identification (ID). The servingcell site will register the mobile ID in a cell location update list.The CLU algorithm for the serving cell site is the following:

IF a CLU for a previously not-registered mobile is received

THEN {register the mobile in the cell location update list; Add atimestamp to the mobile registration record}

ELSEIF a CLU for a previously-registered mobile is received

THEN update the mobile registration record timestamp with the currenttime;

ELSEIF CLUP has elapsed

THEN {scan the cell location update list and purge any records whichhave a timestamp older than Current Time-(CLUP+D)!}

Note the factor "D" is added to CLUP when deciding which records topurge to prevent border cases where a record is purged just before apage for the same mobile is received and before the periodic CLU requestmade it through. For example, D can be 10% of CLUP.

With reference to FIG. 3, it will be appreciated that CLUP correspondsto the "first time period" of step 315. Further, with reference to FIG.4, it will be appreciated that (CLUP+D) corresponds to the "second timeperiod" of step 407.

Moreover, in accordance with the present invention, rather than paging amobile in all cells of a location area, the mobile is paged only in thecells it has visited in the most recent second time period, equal to(CLUP+D). These are the cells which the mobile camped-on during itstraversal of the multiple-cell location area.

As mentioned above in the discussion of FIG. 3, the mobile 100 keepstrack of its most recently-visited cells by maintaining (steps 309 and313) a list of recently-visited cells, corresponding to element 201 inFIG. 2. This list of recently-visited cells 201 comprises the identitiesof the visited cells together with the corresponding times when themobile performed the respective CLU registration procedures. One of thelist entries represents the current cell where the mobile is camped on,and this entry is marked as such.

When a mobile camps on a new cell, it decodes the cell identity in theoutbound control channel and then searches (step 309) for the cell'sidentity in the list of recently-visited cells. A CLU registrationprocedure will be performed (step 311) if the cell does not appear inthe list. A corresponding entry, comprising the cell identity andregistration time, will then be added to the list (step 313).

In addition to the above procedure for adding new registrations, themobile periodically scans the list of recently-visited cells (such as,for example, at a scanning period of CLUP/2). As a result of theperiodic scanning, if the mobile is stationary and remains in the samecell, then a new CLU registration will take place every CLUP time period(step 315), and the entry's registration time will be updatedaccordingly. Also, at each scan, the mobile deletes list entries with aregistration time older than (current time-CLUP). This deletion is donesince these registrations are no longer valid, as the corresponding cellsites have already discarded them (step 407).

When traveling along the boundary between cells, a mobile may repeatedlycamp on the same cells multiple times. Each cell re-selection couldtrigger another CLU registration with the serving cell site, even thoughthe mobile may still be registered in the cell. Such unnecessarymultiple CLU registrations could place a substantial (and unneeded) loadon the inbound control channel of the wireless communication system.

By maintaining the list 201 as described above, the mobile isadvantageously prevented from issuing the unneeded multiple CLUregistrations that otherwise would occur when the mobile travels at theboundary between adjacent cells.

One advantage of the present invention is that it results in a 50%-70%REDUCTION in the air traffic being required for paging. As a furtheradvantage, the invention also results in geographically expandedlocation areas which, in turn, results in up to a 40% REDUCTION in thenumber of switch location updates (SLU's) being required.

In summary, a wireless communication system includes switchinginfrastructure 150 and at least one location area ("LA") having amultiplicity of cells (the "multiple-cell LA") 103. When a mobile 100enters a cell belonging to the multiple-cell LA, the mobile is arrangedwith a cell-registration feature that enables it to register with theserving cell site, thus forming a registration with the cell site. Whenthe mobile enters a further cell belonging to the multiple-cell LA, themobile registers with the corresponding further cell site, thus forminga registration with the further cell site. When the switchinginfrastructure receives a call attempt towards the mobile, the switchinginfrastructure pages the mobile in only those cells in which a cellregistration exists for the mobile.

While various embodiments of the present invention have been describedhereinabove, the scope of the invention is defined by the followingclaims.

What is claimed is:
 1. A method for paging a mobile in a multiple-cellLA in a wireless communication system, the multiple-cell LA including amultiplicity of cells, the wireless communication system includingswitching infrastructure, and wherein the mobile includes acell-registration feature that may be selectively enabled by theswitching infrastructure, the cell-registration feature allowing themobile to form a registration in each cell that it visits, thecell-registration feature thus allowing the mobile to be simultaneouslyregistered in one or more cells of the multiple-cell LA which one ormore cells the mobile has recently visited, the method comprising thefollowing steps, by the switching infrastructure:receiving a callattempt towards the mobile; determining when the cell-registrationfeature is currently enabled for the mobile; and, when it is determinedthat the cell-registration feature is currently enabled for the mobile,paging the mobile in only those one or more cells of the multiple-cellLA in which a registration currently exists for the mobile.
 2. Themethod of claim 1, including the following step, by the switchinginfrastructure:when it is determined that the cell-registration featureis not currently enabled for the mobile, paging the mobile in themultiplicity of cells of the multiple-cell LA.
 3. The method of claim 2,wherein the wireless communication system is a GSM system.
 4. The methodof claim 2, wherein the wireless communication system is an iDEN system.5. The method of claim 2, wherein the wireless communication system isan USDC system.